I'm aware that する is the Japanese verb "To do". In order to conjugate this verb using the Ta form for past tense we of course just replace する with し and add our polite form ます with the た to make しました, so my question is this.

Does this logically make sense to a native Japanese person? If I want to know "Who did it?" as in "Who committed the crime?", "Who did the thing?" etc. Is this sentence really that simple?


1 Answer 1


As you might have learned with respect to the は in the phrase, the Japanese language, and specifically its grammar, is driven by a system of particles. In this case, you have probably yet to learn that there is a particle that corresponds to questions. This is the か particle, and is placed at the end of a sentence or phrase that is meant to be a question. Consider its use to be similar, but not exactly the same, as using a question mark in the English language, and it is voiced.

The か particle transforms a statement into a question, like so:

This is your pencil.

Is this your pencil?

Note that all that changed was the addition of the か particle at the end.

In the case of your not-yet-a-question statement, you'll need to do the same:

Who did it?

This is technically ungrammatical, so you'll need another particle here: the が particle. This particle generally marks the direct subject of the sentence. In this phrase, it replaces the は particle (which can be considered a "topic" particle). Question words in question sentences are automatically the explicit focus of the sentence, so they take the が particle instead of は, when asking a question.

Putting it all together, then we have:

Who did it?

Now this sentence is grammatically correct. There are still more natural ways to express this question, especially depending on the context you'd be asking it in, but without a little more studying from your part, this is as good as this will get.

  • Thanks for the response. Is there a reason we don't need です before the か as in the sentence 「何ですか」 as opposed to 「何か」? Im gonna guess that the です is probably for the polite form? Commented Sep 14, 2018 at 22:56
  • 3
    Just adding that 誰は is categorically ungrammatical - question words must be the sentence focus, and so you can't mark them with the topic particle は. You have to say 誰が.
    – Sjiveru
    Commented Sep 14, 2018 at 23:03
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    @psosuna Thanks! (Technically question words aren't the -subject-, they're the -focus- - you can say 誰に or 誰を just fine)
    – Sjiveru
    Commented Sep 14, 2018 at 23:19
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    @Sjiveru There are however exceptions, for example to show contrast when you're dividing a group entirely into two categories: 「兄さん、じゃもう一つ聞きたいんですがね、人間は誰でも、他人を見て、 誰は生きる資格があって、誰は資格がない、 などとそれを決める権利を持ってるものでしょうか?」 And of course there are set phrases such as 何はともあれ.
    – user1478
    Commented Sep 15, 2018 at 1:53
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    @psosuna です isn't really a verb, though. It doesn't inflect like one, and it doesn't have the same grammatical properties that verbs do.
    – user1478
    Commented Sep 15, 2018 at 2:32

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